TA0038 - RF

TA0038 DC ACCURATE FSK MODULATOR

TA0038
     A typical, low cost, FSK modulator is implemented by injecting the modulation voltage into the phase lock loop of the carrier synthesizer. This is done in two ways, by summing the modulation voltage and the loop error voltage together and applying that to a VCO tuning port. Or, by using a separate tuning port usually havin.

Features

implemented that address this problem. One approach is to predistort the modulation signal to compensate for the effects of the PLL. This has limited results and a finite frequency range. Another commonly used method is to encode the data stream with such techniques as Manchester coding or split phase coding. The basis of this coding is to send two complementary symbols for every data bit, thus a transition is guaranteed for every data bit. This is very effective in that it fixes the lowest frequency component of the modulation signal so that a loop bandwidth can be designed to have a minimal .